I would not consider injector issues with a truck that has that many miles surprising. I am sure a search will reveal many causes to your performance concerns and some repair advice. If the tech that diagnosed your injectors correctly identify three weak injectors it would be wise to replace all eight as any conditions like poor fuel quality or low fuel pressure will have affected the entire set. Replacing only three can make the remaining five show as weak after the repair. You also run the risk of having the remaining injectors fail randomly as well. Inevitably, this will cost you more in the long run due to the labor involved.

Once the injectors are replaced I recommend CHECKING the fuel pressure. You may only need to replace the fuel pressure regulator and both filters. If your truck has a metal aft-axle fuel tank I also recommend that you have the inside of the tank inspected for rust and lining delamination. This will contaminate the system and damage the pump and the injector in a short amount of time.

 

What injectors are bad? If they're all on the same side and you can't afford the entire set, you can just change the 4 on that side and see how it runs. I recently replaced all 8 on mine and i'm about the same mileage as you. It runs like a new truck now. If the bad ones are on the driver's side you can change them yourself pretty easy. I can have those 4 out and sitting on the counter at Ford buying new ones within an hour or hour and a half. Just make sure you have a good torque wrench when you put the new ones back in so you can torque them down to the correct ft pounds.

Drivers side:

Place a clean 5 gallon bucket under the radiator where the drain valve is. Unscrew the drain (3/4 wrench I think) and stand there watching the degas bottle. Once it's drained down enough so that you can't see any coolant in it, tighten the drain valve.
Next, remove the degas bottle. There's 2 bolts holding it up there, then the hoses that go to it.
Remove the big turbo air intake hose that goes from your air filter to the turbo. You'll take out the 2 pieces that lead to the air filter itself.
Now you're down to your FICM. Be gentle with it. It's the silver computer mounted on your valve. Remove it and the brackets that hold it in place. There's 3 plugs on the bottom you'll have to squeeze and pull out.
By now you're staring at the valve cover. Remove the bolts that hold it down and pull it and it's gasket off.
Under it is a high pressure oil rail held down by 8 bolts. Towards the firewall you'll see a big 3/8 screw in the oil rail. This is your stand pipe. Unscrew it and remove the pipe. It's about 9 inches long and has some o rings on it. Now take a T30 torx bit with a 3/8 ratchet and pull the 8 bolts out that hold the rail down. GENTLY pry up on the top of the oil rail with a screw driver (towards the center) using the top of the rocker box as your leverage. When you feel it pop loose, grab ahold of it and lift it up. Let the oil drain out of it down into the rocker box before you remove it.
That's it. You're down to the injectors now.
Take an 18 or 19mm deep socket and use it to push the electrical connectors through their holes in the top of the rocker box after you remove the clip and unplug them from the harness. Next to the injector you'll see a T45 bolt. That's what holds each injector into the head of the engine. Use an extension and 3/8 ratchet with a T45 socket bit and unscrew it. The injector will come out as you unscrew the hold down clamp. Using your index, thumb and middle finger, pull the injector and it's hold down clamp out as one piece.
Pull them all out and that's it.
Before you install the new ones, take some compressed air and blow out the holes that the T45 hold down bolt screws into. There will be oil in them that won't allow you to torque them down correctly.
Put it all back together using a torque ratchet and that's all there is to it. If anyone has anything to add feel free.

 

A picture says a thousand words....:thumb:

 

If they're on the passenger side it's basically the same process only a little tighter area to work in due to the HVAC box being in the way over there. You can save several hundred dollars in labor by learning to change them yourself. Unfortunately the cost of the injectors themselves are $267 each which is the biggest part of the expense.

 

Soooo, how much would you charge to replace all 8 on my 2003?